1. Field of the Invention
The present invention relates to an electric member having a plurality of leads and a method of manufacturing the electric member.
2. Description of Related Art
A typical remote-controlled light receiving module 4 for receiving infrared light conveying a remote control signal from a remote commander is shown in FIGS. 1A and 1B.
Reference numeral 1 shown in the figures is a package having an approximately cubic shape. The package 1 is made of resin which can be penetrated by the infrared light. A remote-controlled receiver IC which is not shown in the figure is sealed inside the package 1. Reference numeral 2 is a lens having a convex spherical surface created as an integrated part of the front surface of the package 1. The lens 2 is fixed at a location which is optimum for focusing the infrared light modulated by the remote control signal at the remote commander on the light receiving surface of the remote-controlled receiver IC.
Reference numeral 3 denotes a lead protruding from the bottom surface of the package 1 in a direction perpendicular to the bottom surface. In the conventional remote-controlled light receiving module 4, the shapes and the sizes of the sectional surfaces of the leads 3 are uniform at least at the bottom surface of the package 1 from which the leads 3 protrude. The leads 3 are created so as to extend straight out from the bottom surface of the package 1.
Such a remote-controlled light receiving module 4 is used in remote-controlled equipment such as a television receiver, tape recorder and air conditioner. Speaking in concrete terms, it is necessary to insert the external tips of the leads 3 of the remote-controlled light receiving module 4 into predetermined lead inserting through holes on a printed wiring board and solder the leads to wires on the board.
FIG. 2 shows how the conventional remote-controlled light receiving module 4 is typically mounted on a printed wiring board. Reference numeral 5 shown in the figure is the printed wiring board whereas reference numerals 6 each denote a lead inserting through hole created on the printed wiring board 5 for inserting a lead 3. Reference numeral 7 denotes a piece of solder for connecting a lead 3 inserted into a lead inserting through hole 5 to wiring on the printed wiring board 5.
Reference numeral 8 is a socket for enclosing the remote-controlled light receiving module 4. The socket 8 serves as a component for fixing the position of the remote-controlled light receiving module 4, in particular, the height of the remote-controlled light receiving module 4 above the surface of the printed wiring board 5. In addition, the socket 8 is also used for fixing the orientation of the remote-controlled light receiving module 4, in particular, the direction of the optical axis thereof. That is to say, since the remote-controlled light receiving module 4 exhibits a directivity characteristic, the position and the optical axis thereof are very important factors which affect the way the infrared light is received from a remote commander modulated by a remote control signal of an optical apparatus. It is thus necessary to install the remote-controlled light receiving module 4 on the printed wiring board 5 in a way determined in advance.
As described earlier, in the case of the conventional remote-controlled light receiving module 4 shown in FIG. 1, the shapes and the sizes of the sectional surfaces of the leads 3 are uniform at least at the bottom surface of the package 1 from which the leads 3 protrude. The leads 3 are created so as to stretch straight out off the bottom surface of the package 1. Therefore, even with the leads 3 inserted into the lead inserting through holes 6, the conventional remote-controlled light receiving module 4 is still shaky to a certain degree due to a gap existing between the conventional remote-controlled light receiving module 4 and the printed wiring board 5. As a result, the position and orientation of the conventional remote-controlled light receiving module 4 relative to the printed wiring board 5 are not truly fixed. For this reason, loosening and a positional shift are generated inevitably in the conventional remote-controlled light receiving module 4. Loosening refers to an inclination or slope of the optical axis relative to a set direction. Such a slope is undesirable in an optical system. It is needless to say that the positional shift is also undesirable as well. In order to avoid such loosening and such a positional shift, the socket 8 is used for firming the position and the orientation of the remote-controlled light receiving module 4.
The socket 8 has an installation pin 9 to be inserted into a lead inserting through hole 6. Reference numeral 10 is a hook nail 10 formed at the end of the installation pin 9 for hooking the installation pin 9 at the back surface (or the surface on the side not facing the socket body) of the printed wiring board 5. Reference numeral 11 is a stopper created on the installation pin 9 at a position separated from the hook nail 10 at the end of the installation pin 9 by a distance about equal to the thickness of the lead inserting through hole 6. The stopper 11 is used for hooking the installation pin 9 on the front surface (or the surface on the side facing the socket body) of the printed wiring board 5. By hooking the installation pin 9 on the printed wiring board 5 by means of the stopper 11 and the hooking nail 10, the position, particularly the height above the printed wiring board 5, and the orientation of the socket 8 itself are fixed. The socket 8, in turn, firmly sustains the position and orientation of the remote-controlled light receiving module 4. That is to say, the position and orientation of the remote-controlled light receiving module 4 relative to the printed wiring board 5 are fixed in a prescribed manner using the socket 8. At this position and in this orientation, the leads 3 of the remote-controlled light receiving module 4 are soldered to wiring on the printed wiring board 5.
The problems described below are encountered because the position and orientation of the conventional remote-controlled light receiving module 4 shown in FIGS. 1A and 1B are fixed by using the socket 8.
First of all, there is a problem that the cost is increased by the use of the socket 8.
To be more specific, efforts need to be made to reduce the number of components and the number of assembly operations in response to a very strong demand for low-cost remote-controlled equipment such as a television set. In spite of such a demand, the conventional remote-controlled light receiving module 4 employs the socket 8 merely for firming the position thereof. The use of the socket 8 cannot thus be tolerated.
A second problem is that, since the position of the remote-controlled light receiving module 4 is fixed by the socket 8 through dip soldering, the leads 3 are pulled by the tensile stress of the solder 7 during dip soldering, giving rise to a problem that stress is applied to an IC pellet die-bonded to one of the leads 3. It should be noted that the IC pellet itself which is embedded inside the package 1 is not shown in the figure. This problem is described in more detail as follows.
With the position of the conventional remote-controlled light receiving module 4 fixed by the socket 8, the leads 3 are soldered by using a dip-soldering technique. As the solder 7 becomes cool, it shrinks. The shrinking force pulls the leads 3 in a direction indicated by an arrow a shown in FIG. 2.
Since the position of the package 1 is fixed by the socket 8, however, the leads 3 cannot move in the direction indicated by the arrow a. As a result, the leads 3 are inevitably pulled out away from the package 1 downward to the lower side shown in FIG. 2. The IC pellet die-bonded to one of the leads 3, in turn, experiences stress developed by the package 1 for sealing the IC pellet. The application of stress to the IC pellet gives rise to characteristic deterioration, reliability deterioration and an increased failure rate of the IC which are of course undesirable.